1. Field of the Invention
The present invention relates to a battery. More specifically, the present invention relates to a structure of a battery including an electrode body, a battery case in which to accommodate the electrode body, and an insulator film that insulates (isolates) the electrode body from an inner wall of the battery case.
2. Description of Related Art
In recent years, nonaqueous electrolyte secondary batteries such as a lithium-ion secondary battery (lithium secondary battery) and a sodium-ion secondary battery have been used as a so-called portable power supply for a PC, a portable terminal, or the like, and as a vehicle drive power supply because the nonaqueous electrolyte secondary batteries are lightweight and have a high energy density as compared with existing batteries. Particularly, the lithium-ion secondary battery that is lightweight and has a high energy density is preferably used as a high-output power supply for driving vehicles such as an electric vehicle (EV), a hybrid vehicle (HV), and a plug-in hybrid vehicle (PHV).
As this type of battery, there has been known a battery structure including an electrode body configured such that a positive electrode including a positive-electrode active material layer on a positive-electrode current collector and a negative electrode including a negative-electrode active material layer on a negative-electrode current collector are laminated via a separator. In such a battery, respective active material layer non-forming parts that do not include active material layers are provided in respective end portions (that is, end portions of the electrode body) of the positive-electrode current collector and the negative-electrode current collector. A positive electrode inner terminal and a negative electrode inner terminal are connected to the respective active material layer non-forming parts, and those respective inner terminals are electrically connected to a positive electrode external terminal and a negative electrode external terminal for external connections.
Such a battery is generally formed such that an electrode body and a battery case are manufactured separately, and then, the electrode body is accommodated in the battery case. From the viewpoint that a physical strength is large, a metal package is often used as the battery case. In this case, in order to insulate the metal battery case from the electrode body, such a technique is used that the electrode body is insulated (isolated) from an inner wall of the battery case by use of an insulating film, for example. For example, Japanese Patent Application Publication No. 2010-113816 (JP 2010-113816 A) describes a battery including such an insulator film.
In the meantime, the battery including the insulator film is generally formed such that the electrode body and the insulator film are accommodated in the battery case from an opening provided in the battery case (a battery case main body), and then, the opening is sealed (typically, welded) by a cover. At this time, if the insulator film is sandwiched between the opening of the battery case and the cover, poor sealing (poor welding) may occur. Accordingly, a size of the insulator film is typically set to be small, so that the insulator film does not reach the opening of the battery case. In the meantime, if the insulator film the size of which is set to be small as such is used, a region where the electrode body (or an inner terminal connected to the electrode body) is not insulated from the inner wall of the battery case by the insulator film may occur in the vicinity of the opening in the inner wall of the battery case. On this account, in such a non-insulating region, an internal short-circuit may occur between the battery case and the electrode body (or the inner terminal connected to the electrode body). For example, in the non-insulating region, it is conceivable that the battery case and the electrode body (or the inner terminal connected to the electrode body) are electrically connected to each other (make electrical contact with each other) via a foreign matter (e.g., a metallic piece). In the battery configured such that a positive electrode external terminal and a negative electrode external terminal are provided in the cover, the positive electrode inner terminal and the negative electrode inner terminal that electrically connect the external terminals to the electrode body are at least partially placed in the non-insulating region in general. In view of this, such a technique to improve insulating properties between the inner terminals (particularly, parts of the inner terminals, the parts being placed in the non-insulating region) and the battery case has been desired.